Disorders of the retinal vasculature are major factors in many retinal diseases, but basic understanding of the control of retinal vascular pressure and the mechanics of blood flow through retinal capillaries is lacking. The applicant proposes to continue use of the servonull micropuncture technique to study the control of microvascular pressure and capillary flow in the retina. Additionally, a new high resolution intravitreal imaging system for visualizing the retinal capillaries will be used. Three lines of study are proposed. In the first line of study, the applicant will complete his basic studies of the control of retinal vascular pressures, and in the second he will begin to examine the factors that control flow at the capillary level. The third line of effort will involve development of a mathematical model of the retinal circulation as a framework for understanding retinal circulation. Conditions to be imposed to study their effects on vascular parameters will include elevated intraocular pressure, isovolemic hemodilution, hyperglycemia, vascular occlusion and other manipulations designed to illuminate fundamental mechanisms and sites of retinal vascular function. Cats are used in these studies because of the comparative similarities of their retina and retinal vasculature to that in humans. The findings are expected to have implications for retinal diseases with circulatory components such as glaucoma, diabetes and retinal occlusive disease.